The invention relates to a superconducting structure, comprising a plurality of band-segments of band-shaped superconductors, wherein each band-segment has a substrate and a superconducting layer deposited onto it, and wherein the band-segments are joined to one another by superconducting layers that face each other.
US 2005/0173679 A1, for example, discloses such a superconducting structure.
Superconductors can carry electrical currents practically without any ohmic losses. They are especially deployed where high electrical currents are required, for example, in magnet coils.
Superconductors can only conduct electrical current without losses below a critical temperature (also called transition temperature). Above this temperature, the superconductor enters a normally conducting state.
Metal superconducting materials, such as NbTi, which can be processed as wires, have a relatively low critical temperature (for NbTi, for example, it is about 9K), making their use quite expensive, especially with respect to the necessary cooling. Moreover, metal superconductors have relatively low critical magnetic fields, above which they lose their superconductive properties.
High-temperature superconductors (HTSL), such as yttrium barium copper oxide (YBCO), have significantly higher critical temperatures, YBCO for example, about 90K, but are difficult to process due to their ceramic properties. If they are used at temperatures significantly below their critical temperature, HTSLs can conduct comparatively large currents, i.e. they have a high critical current density. With their comparatively high critical magnetic field strengths, these materials are also suitable for low operating temperatures in strong magnetic fields.
For technical applications, HTSLs are usually deposited as a thin layer onto band-shaped, usually metal substrates, wherein, as a rule, one or more buffer layers are interposed between the substrate and the superconducting layer, and one or more final metal layers are deposited on top of the superconducting layer. This type of construction is also termed a band-shaped superconductor and has commonly become known as a “coated conductor” in English.
However, depositing superconducting layers of good quality is relatively difficult. As a rule, substrate surfaces with a special texture are required, which can only be provided over limited lengths. Currently, good-quality band-segments of band-shaped superconductors are limited to a maximum range of approx. 100 to 200 m.
EP 0 545 608 A2 proposes joining conductor segments, which can only be manufactured in good quality in limited lengths, in order to enable current to be transported over longer distances, for instance, several kilometers.
US 2005/0173679 A1 discloses the joining of two band-segments of band-shaped superconductors, wherein the superconducting layers on the respective substrates face each other. The superconducting layers are to be in superconducting contact and the proximity of the two polycrystalline superconducting layers is intended to increase the effective grain boundary surface and thus improve the critical current.
U.S. Pat. No. 6,828,507 B1 also discloses the joining together of two band-segments of band-shaped superconductors, wherein the superconducting layers on the respective substrates face each other. The superconducting layers are joined by means of one or more normally conducting intermediate layers (for instance, covering layers of the individual band-segments).
The object of the invention is to provide a superconducting structure, which exhibits a high current-carrying capacity and which is also suitable for long distances.